Tunable electrically small antenna



March 19, 1968 R. c. FENWICK 3,374,483

TUNABLE ELECTRICALLY SMALL ANTENNA Filed May 6, 1965 6/\ h 7/ TRANSCEIVER 59 INVENTOR.

62 RICHARD c. FENWICK BY %m ATTORNEY United States Patent 3,374,483 TUNABLE ELECTRICALLY SMALL ANTENNA Richard C. Fenwick, Richardson, Tex., assignor to Coliins Radio Company, Cedar Rapids, Iowa, a

corporation of Iowa Filed May 6, 1965, Ser. No. 453,801 6 Claims. (Cl. 343895) ABSTRACT OF TfiE DISCLGSURE A space saving implementation of an electrically small This invention relates in general to antennas and in particular to a spiral wound antenna.

It is desirable at times to construct an antenna which is as small as possible so as to eliminate large structures which might be subject to adverse icing and wind resistance. The present invention relates to a half-wave conductor formed into a spiral and which has a movable contact that allows the half-wave length of the antenna to be varied.

It is an object of this invention to provide an improved compact antenna.

Another object is to provide a simple construction which allows an antenna to be cheaply and easily manufactured.

Further objects, features, and advantages of this invention will become apparent from the following description and claims when read in view of the accompanying drawings, in which:

FIGURE 1 is a schematic illustration of a pair of short monopoles separated by a half-wave length antenna;

FIGURE 2 is a top view of a spiral-shaped antenna according to this invention;

FIGURE 3 is a side view of the antenna shown in FIGURE 2;

FIGURE 4 is an enlarged detailed sectional view of the slide contact of this invention; and,

FIGURE 5 is a modification of the invention illustrating a pair of spirals connected together to form a composite antenna.

FIGURE 1 illustrates a ground plane designated generally as 10. A conductor 11 has one end connected to the ground plane and the other end connected to a conductor 12 which is parallel to the ground plane 10. An energizing source 13 has a pair of slide contacts 14 and 16 which are engageable with the conductor 12 and the ground plane 10. The distance between the contact 14 and the monopole 11 is a half-Wave length at the resonant frequency of the antenna thus formed. By moving the energizing means 13 along the conductor 12, the frequency of the antenna may be increased or decreased as desired. Thus by moving the energizing means 13 toward the monopole 11, the frequency will become higher and, alternatively, by moving the energizing means 13 and cnotact 14 away from the monopole 11, the frequency will be lowered.

Monopoles separated by half-wave length conductors 3,374,483 Patented Mar. 19, 1968 as shown in FIGURE 1 comprise antennas which are very efficient.

FIGURES 2, 3 and 4 illustrate a practical embodiment of the antenna in FIGURE 1.

A ground plane 21 has standoffs 22 and 23 attached to it for supporting an insulating plate 24. A spirally wound conductor 26 is attached to the plate 24 by spiral support 27. This is best shown in FIGURE 4. Conductor 26 engages the end 28 of a telescoping slide contact 29. The end 28 is formed with an outer U-shaped member 31 which is lined with Teflon material 32. A wiper spring 33 is mounted in member 31 and is electrically connected to the end 34 of wiper contact 29. The spring contact 33 makes electrical contact with the face 36 of the spiral conductor 26.

As best shown in FIGURE 3, the telescoping contact 29 is rotatably connected to a support 37. A transceiver 38 has one output lead 38 connected to the ground plane 21 and the other output lead 41 connected to the support member 37 and to the telescoping arm 29. A knob 42 is connected to a shaft 43 which extends through the support 37 and is connected to the telescoping arm 29 to rotate it. Telescoping arm 29 is formed of a number of telescoping sections 44, 46, 47 and 48. Electrical continuity is maintained between lead 41 and contact 33.

In operation, the outer end 49 of the spiral conductor 26 is connected to the ground plane by a lead 51. The lead 51 corresponds to the monopole 11 in FIGURE 1. The point of engagement of the spring contact 33 of the telescoping wiper contact 29 determines the length between the monopole 11 and the wiper contact 14. In other words, the half-wave length distance is indicated in FIGURE 2 between the ground point 51 and the wiper contact 29. Thus, a simple and compact antenna is formed which may by tuned by the knob 42 which rotates contact arm 29 to vary the half-wave length distance between ground point 51 and the position of the contact 33.

A modification of the invention is illustrated in top view FIGURE 5, wherein a ground plane 52 is electrically connected by lead 53 to a telescoping contact 54 which engages a spiral conductor 56. The wiper contact 54 is similar to contact 29 shown in FIGURES 2, 3 and 4 and the conductor 56 is similar to the conductor 26 shown in FIGURES 2, 3 and 4. A second spiral conductor 57 is mounted adjacent conductor 56 and has a telescoping wiper contact 58 which is electrically connected by lead 59 to the output of a transceiver 61. The other output lead 62 of the transceiver is connected to the ground plane 52. The end 63 of conductor 57 is connected by a conductor 64 to the end 66 of the spiral conductor 56.

Shafts 68 and 69 are connected to wiper contacts 54 and 58, respectively, to rotate them. The shafts 68 and 69 are connected into a suitable gear box 71 and a knob 67 is attached to box 71. As knob 67 is turned, the electrical distance between the wiper contacts 54 and 58 will be lengthened or shortened depending on the direction of the rotation of the knob 67. To increase the length between contact 58 and point 63 of the spiral 67, the contact 58 must be rotated clockwise. To increase the length from point 66 to wiper contact 54, the contact 54 must be rotated counterclockwise to shaft 68. Thus, gear box 71 causes shaft 68 to turn clockwise when shaft 69 turns counterclockwise. Alternatively, when the shaft 69 is rotated clockwise, shaft 68 rotates counterclockwise.

The active lengths of the spirals 56 and 57 comprise quarter-wave lengths at the resonant frequency of the antenna and the distance between the contacts 54 and 58 will therefore be a half-wave length. This allows an antenna to be formed in a relatively small space.

'It is seen that this invention provides a compact and efficient antenna. Although it has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are Within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. An antenna comprising a ground plane, support means attached to said ground plane, a spiral conductor supported by said support means, one end of the spiral conductor connected to said ground plane and the other end of said conductor being free, a wiper conductor engageable with the spiral conductor and movable thereto, feed points for the antenna connected to the wiper contact and said ground plane, said wiper contact being formed of a guide member engageable with said spiral conductor and a telescoping arm attached to said guide member, and a shaft attached to one end of said telescoping arm with the shaft supported for rotary motion at the center of said spiral conductor.

2. An antenna comprising a ground plane, support means attached to said ground plane, an insulated plate attached to said support means, a spiral conductor attached to the insulated plate, one end of said spiral conductor electrically connected to said ground plane, a wiper contact engageable with said spiral conductor and movable relative thereto, said wiper contact comprising an engaging end for mechanically and electrically contacting said spiral conductor, a telescoping arm attached to said engaging end, and the other end of said telescoping arm rotatably supported adjacent of said spiral conductor.

3. In apparatus according to claim 2 means for rotating the telescoping arm to vary the contact point on the spiral conductor.

4 I g 4. An antenna comprising a pair of coplanar spiral conductors arranged at equal distance from a ground plane with the outer ends of said spiral conductors con-' nected together, a pair of Wiper contacts each engageable with one of said spiral conductors, means for moving the wiper contacts relative to the spiral conductors, one of said wiper contacts being connected to said ground plane and the other of said wiper contacts and said ground plane comprising respectively feed points for said antenna.

5. In apparatus according to claim 4 wherein said wiper arms are caused to move with respect to their associated spiral conductors so as to simultaneously effect a length of each spiral conductor between its associated wiper arm and the common connection between the outer ends of said spiral conductors equal to approximately onequarter Wavelength as defined by the operating frequency of said antenna.

6. In apparatus according to claim 5 wherein said spiral conductors are wound with respective opposite senses.

References Cited UNITED STATES PATENTS 1,530,684- 3/1925 lMauborgne et a1. 343895 1,553,315 9/1925 Gould 343-870 XR 2,431,124 11/1947 Kees et a1. 343845 XR 2,758,300 8/1956 Dylewski 343-84-5 3,151,328 9/1964 Boyer 343-748 XR 3,152,330 10/ 1964 Chatelain 343-895'XR ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBAOH, Examiner.

M. NUSSBAUM, Assistant Examiner. 

